CMake: Fix git-qt-foreach output being lost in non-tty invocations

There's a tty check in qt_internal_foreach_repo_run.
The code reads tty_exit_CODE rather than the correct tty_exit_code.

In a non-tty context (when stdout is a pipe), /usr/bin/tty prints
"not a tty" and has a non-zero exit code, leading to stdout being
redirected to a file named "not a tty" in every submodule.

Use the right name.

Pick-to: 6.8
Change-Id: I6bba544aa0e3bbe2f09925cae56f303e70643681
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
(cherry picked from commit 8e218fec47)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 58e5ed9147)

cmake/QtTopLevelHelpers.cmake

@@ -1386,7 +1386,7 @@ function(qt_internal_foreach_repo_run)
 
     set(color_supported FALSE)
     set(output_goes_where "")
-    if(NOT tty_exit_CODE AND tty_name)
+    if(NOT tty_exit_code AND tty_name)
         set(color_supported TRUE)
         set(output_goes_where "OUTPUT_FILE" "${tty_name}")
     endif()